The present invention relates to a textile yarn piecing device with an evaluation arrangement for determining parameters of an automatic yarn piecing process, and more particularly to such a piecing device having at least one sensor device for measuring the yarn diameter and for detecting the position of a respective measuring point in relation to the yarn piecing created.
As demands have been increasingly made on the yarn production process, continuously higher demands are being made on the creation of yarn piecings formed in the yarn production process. Following yarn breaks, the process of creating piecings and the subsequent re-start of the spinning process is usually performed at the individual spinning stations of the open-end rotor spinning frames by a piecing device, often referred to as a piecing cart, which travels along the spinning frames.
For example, following a yarn break, which triggers the piecing process, the time before spinning is re-started again at the spinning station is of varying length. The delivery of sliver is deactuated when the yarn break occurs. However, the opening roller continues running and continues to separate fibers from the sliver previously fed. In order to produce uniform conditions for the spinning re-start, the fiber feed from the sliver is equalized before every spinning start to achieve as uniform as possible a pre-feeding amount of sliver. Spinning starts with the start of rotation of the rotor. A control device, for example a microprocessor, calculates the acceleration required for the rotor to reach operating speed from pulses detected as a function of the number of rotor revolutions, so that a preset number of revolutions of the rotor for the spinning start is reached after a constant amount of time, and determines the time of starting the pre-feeding of sliver based upon the acceleration. Fibers are again combed out of the sliver and are aspirated over the edge of the stopped rotor during the time following the equalization of the fiber presented from the sliver and the time of re-actuation of the delivery device for the operational fiber feed. This causes a certain delay in achieving the required fiber flow and possibly a thinner extent of yarn downstream of the yarn piecing during the acceleration of the fiber delivery device to its delivery speed. Pre-feeding of fiber takes place during a predetermined time and is deactuated thereafter. In the course thereof, it is also possible to control the amount of delivered fibers by setting the delivery speed, besides the length of pre-feeding. Following the deactuation of fiber pre-feeding and the return of the trailing end of the broken yarn, i.e., the so-called upper yarn, the fiber delivery is turned on again shortly prior to the start of the fiber withdrawal in order to compensate for the delay. The amount of fibers now fed into the rotor is placed on top of the previously delivered amount of fibers in the rotor. Starting of the fiber withdrawal takes place after a defined amount of dwell time of the yarn in the rotor groove, during which the end of the upper yarn to be connected has time to break open the ring of fibers in the rotor and to become connected with the delivered fibers. The yarn withdrawal speed is set to a value corresponding to the instantaneous number of rotor revolutions while maintaining the desired yarn twist. Up to the point at which the operating number of rotor revolutions is achieved, the yarn withdrawal speed follows the increase in the number of rotor revolutions. Besides the continued running of the fiber flow after the delivery has been deactuated, and the delayed actuation of the delivery, the flow of fibers can also react with a delay during the increase of the delivery speed. This can lead to the yarn becoming too thin while the rotor is being accelerated. In particular, this occurs distinctively at low delivery speeds.
To prevent this undesired deviation from the desired yarn thickness, it is possible to perform a supplementary delivery of additional fiber. In the course thereof, the delivery speed of the fiber feed device is increased over a set value in order that the respectively required amount of fibers arrives in the rotor. A thinner extent in the yarn can also still occur even with the performance of a supplementary delivery of additional fiber, if the latter is performed to an insufficient extent. If the supplementary delivery of additional fiber is of too large a size, a thick place is caused in the yarn, which is also undesired. Efforts are therefore made to make the amount of the supplementary delivery of additional fiber as accurate as possible from the start. With the increasing feed path of the sliver, the addition is reduced. The supplementary delivery of additional fiber is terminated after a delivery length, which corresponds to the staple length, has been achieved. Starting at this time, the amount of fiber is delivered without any supplementary delivery of additional fiber. Such supplementary delivery of additional fiber during the start of spinning have been described, for example, in German Patent Publication DE 40 30 100 A1, or in the publication by Raasch et al., entitled: xe2x80x9cAutomatisches Anspinnen beim OE-Rotorspinnenxe2x80x9d [Automatic Piecing in Open-End Rotor Spinning], in MELLIAND Textilberichte [Textile Reports], April/1989, pp. 251 to 256.
The demands made on the accuracy of the lengths of such additional deliveries of fiber have been noticeably increased because of the increasing requirements made on yarn quality, and in particular with the demands for greater spin drafting and smaller rotors. With a draft of 100 times, an error of 0.5 mm in determining the length of the supplementary delivery of additional fiber causes an error in relation to the yarn of 50 mm in length. With 350-times the draft, this error affects a length of 175 mm of the yarn. These examples clearly illustrate how great the demands made on accuracy are when determining the length of a supplementary delivery of additional fiber.
In accordance with the above mentioned prior art, the first piecing is already created with a supplementary delivery of additional fiber. In this manner, it is intended to prevent thinner extents, along with the danger of yarn breaks and interruptions during the spinning start connected with this supplementary delivery of additional fiber. To determine the supplementary delivery of additional fiber, an empirical value is employed, which is a function of the average staple length of the fibers used. While the staple length of synthetic yarn is known, the staple length of cotton or mixed yarns can only be determined with sufficient accuracy by means of extensive laboratory tests. Since the staple length is proportionally a part of the determination of the length of the supplementary delivery of additional fiber, deviations between the staple length used for the calculations and the actual staple length lead to errors in the determination of the length of the supplementary delivery of additional fiber, which has the above described results and in particular have a special effect in case of long drafts.
Further criteria, for example the clothing of the opening roller, the number of revolutions of the opening roller and the rotor acceleration time (with its effects on the comb-out time), have an effect on the required extent of the supplementary delivery of additional fiber. However, this effect can only be determined empirically, by means of generating and evaluating a large number of further piecings. Thus, a sufficiently exact size of the supplementary delivery of additional fiber for a qualitatively satisfactory piecing can only be determined following a relatively elaborate, and in particular time-consuming, optimization phase. The optimization requires the manual intervention of the operators. The quality of the results is definitely dependent on the experience of the operators.
It is accordingly an object of the present invention to provide improvements in the creation of a yarn piecing.
In accordance with the invention, this object is attained by means of a piecing device equipped with a control device which is operative to perform a testing phase during which at least one test piecing is created without any supplementary delivery of additional fiber. The length of a thinner extent created downstream of the test piecing (as viewed in the traveling direction of the yarn) is determined and the extent of the supplementary delivery of additional fiber is determined from the measured length of the thinner extent. In this manner, it is possible to obtain high-quality piecings immediately following the start of the spinning operation by means of a single setting of piecing parameters in the test phase, which are distinguished by the greatest possible matching of the upper yarn diameter and the diameter of the newly spun yarn section adjoining the piecing.
It has been surprisingly shown that the optimization phase in connection with the creation of yarn piecings is not lengthened by the additional testing phase creating test piecings, but is clearly shortened. In this manner, the supplementary delivery of additional fiber can be very precisely determined.
The above mentioned prior art demonstrates that, by the employment of empirical values in connection with piecing parameters, an attempt is made to already prevent thinner extents when creating the first piecing, or at least to reduce such thinner extents, and to make the yarn uniform in the area of piecing. This is intended to prevent interruptions and to increase productivity. The piecing optimization is not only clearly accelerated by means of creating a test piecing in a test phase and the subsequent removal of the test piecing as contemplated by the present invention, but in addition the yarn produced in the course of the spinning operation already exclusively contains high grade piecings and therefore is of an increased yarn quality from the start. Also, the degree of automation of the automatic piecing operation can be increased with an embodiment in accordance with the present invention. The operators are thereby relieved so as to be available for other jobs.
The size of the supplementary delivery of additional fiber is a function of the length of the supplementary delivery of additional fiber. The length of the thinner extent, which is used to draw conclusions regarding the length of the supplementary delivery of additional fiber, can be determined by the evaluation of the measured yarn diameters. For this purpose, the yarn diameters measured in the area of the thinner extent can be compared with a reference diameter derived from the diameter of the upper yarn, and the end of the thinner extent, and accordingly the length thereof, can be determined when a match has been detected. The comparison can be performed by means of a comparator. It is alternatively possible to determine the mean rise of the curve path in the end area of the thinner extent by the course of the diameter determined by means of the measured diameter values and represented as a curve path plotted over the yarn length, and the intersection of the mean rise and the comparison diameter derived from the upper thread diameter can be determined to be the termination of the thinner extent.
By means of a reduction of the draft effective during the test phase it is possible to prevent the thinner extent downstream of the test piecing becoming so thin as to present a risk of a yarn break and therefore to prevent the case where a measurable test piecing, or a measurably thinner extent would no longer be available. The draft reduction in addition makes it possible that, even with large drafts, the yarn assuredly assumes or reaches the comparison diameter derived from the standard yarn thickness within a limited window for piecing check measurement, and that therefore the measurement of the thinner extent can take place in every case.
An algorithm, which takes into consideration the staple length and a limited, preselected measurement range for measuring the yarn diameter, advantageously permit the simple, rapid and automated determination of the minimum size of the draft reduction. For this purpose, the staple length can also be determined only approximately without disadvantageous results. To this end, the parameters can be previously provided to the control device or a computer installation connected with the control device, or the parameters can be called up out of a data memory.
In case of nominal drafts, for example wherein the draft lies between fifty times and one hundred times and wherein the algorithm taking the staple length and the limited measurement area for measuring the yarn diameter into consideration does not result in any draft reduction or in just a slight draft reduction, it is possible to determine the reduced draft in a simplified way by multiplying the nominal draft with a preselected factor which is slightly less than one.
An increase in the precision of the result of the evaluation is achieved if several test piecings with the same preselected parameters are checked, and if a mean profile for the piecings of thinner extent is formed from this evaluation thereafter or continuously. Natural fluctuations in the sliver or the fiber mixture, as well as scattering caused by the differences in the spinning means, are thereby included in the evaluation. It is simultaneously possible by means of averaging to produce a smoothing of the piecing profiles, whereby the measurement of the thinner extents can take place more easily, precisely and dependably. For this purpose, the test piecings can be created at several different spinning stations.
The increased demands on accuracy made with increasing nominal drafts in the course of the determination of the supplementary delivery of additional fiber, and therefore on the precision of the piecing profile, are taken into account in that the number of test piecings used for forming the mean values is also increased with a rise in the nominal draft.
A check of the automatic evaluation of piecing profiles can be advantageously performed in the testing phase by means of a device for displaying of the piecing profiles, for example as the piecing repetitions occur, or during the deactuation of spinning stations during piecing.
By means of the present invention, it is possible to significantly reduce the optimization phase when creating piecings, and to improve the piecing profile. The invention represents a step in the direction toward an automatic service device, for example a piecing cart, which calibrates and optimizes itself on the basis of the quality data determined by the piecing checking device. By means of the invention, it is possible to advantageously increase productivity, and therefore also the efficiency of the yarn production process, as well as the yarn quality.
Further details, features and advantages of the invention will be explained and understood from the following disclosure of a preferred embodiment of the invention with reference to the illustrations in the accompanying drawing figures.